My Mac runs slowly with sudden crashes sometimes until I learned the corespotlightd that consumes high CPU usage was the troublemaker. I tried reinstalling macOS, but it seems like just a temporary way. By accident, I found Connie's post about the fixes for this issue. I don't know which way helps me out, as I followed all the ways she mentioned. If you are also running into the same issue, I hope my sharing will give you some help!